In a rack-and-pinion steering system, the steering pinion is rotatably connected to the steering column, operable by the steering wheel of the vehicle, and this pinion engages the rack slidably mounted in an elongate steering casing. The two ends of the rack, external to the casing, are coupled to steering tie rods associated respectively with the right and left steered wheels of the vehicle. Thus, the rotation of the steering wheel in either direction is transmitted by the steering column to the steering pinion, and is converted into a corresponding translation of the rack which, via the steering tie rods, causes by itself the coordinated orientation of the two steered wheels of the vehicle, for a steering to the right or to the left.
In such a steering system, the push member device resiliently acts on the back of the rack, in the region of the steering pinion, for strongly pressing the toothing of this rack against said pinion, thus avoiding any risk of loss of contact of the toothings. The push member device is usually in the form of a push member line, with a movable part forming a friction pad, guided in translation and biased by resilient means toward the back of the rack.
There are also known the eccentric push member devices, which replace the conventional linear push member concept with a rotating concept. In such a device, there is provided an annular or arcuate rotating pad which has a circular outer periphery and an inner periphery which is also circular but eccentric relative to its outer periphery. The rotating pad is rotatably mounted in the steering casing, about an axis of rotation parallel to the longitudinal axis of the rack. The eccentric inner periphery of this pad bears against the back of the rack. The rotating pad is rotatably biased or is angularly positioned so that its inner periphery, applied against the back of the rack, pushes back the latter toward the teeth of the pinion so as to maintain engagement of the toothings.
In particular, the French patent FR 2 951 797 or its international equivalent WO 2011048328, in the name of the Applicant, describes an eccentric push member device, as recalled above, in which a clearance compensation mechanism comprises a push member bearing on a radial arm of the rotating pad under the effect of a compression spring inserted between the pusher and a fixed support of the pad, or an element integral with said support. A movable stop, rotatably mounted relative to the support or to said element, includes toothings with stepped teeth which cooperate with notches of the pusher. The movable stop is connected via a torsion spring to the support or to the element integral with the support. Thus, the notches successively cooperate with the stepped teeth of the toothings of the movable stop, so as to take up the mechanical clearance due in particular to wear.
In the embodiment described in the aforementioned documents, the rotating pad is rotatably mounted and guided on a support mounted in turn in the steering casing. This support includes an arcuate cradle, on which the outer periphery of the rotating pad bears in a sliding manner.
Trivially, the arcuate cradle of the support, on the one hand, and the outer periphery of the rotating pad, on the other hand, are both cylindrical, one is concave and the other is convex. The drawback of such an embodiment is that in addition to the relative sliding movement between the outer periphery of the pad and the cradle, there also occurs a relative rolling movement due to the manufacturing clearances. This may lead to the occurrence of noise and to a disturbance of the kinematics of the clearance compensation mechanism, in particular when the load applied on the pad changes direction and amplitude.